Various network-based search applications allow a user to enter search terms and receive a list of search results from different information sources. The content of the results may change over time such that the information, such as images, provided in response to the search may not be current. For example, an image provider may provide landscape images. As the landscape changes over time, for example where a dilapidated building leveled, a retail establishment closes, a new home is constructed on a previously vacant lot, or other variations occur due to seasonal or daylight changes (e.g., summer vs. winter, day vs. night), at least some of the previously captured images will become stale because the landscape images may not reflect a current version of the location. If the imagery corresponding to these locations is not updated to reflect the changes, then users may be provided with stale or out of date images for the location.
In another example, an image provider may provide areal images of a location. As the landscape of the area changes over time, at least some of the captured images may become stale. For example, trees may have been cleared as a precursor to construction of a new road. Accordingly, any images that include these trees may be considered stale and any images that show the cleared area but not the new road may soon become stale. If the images that correspond to these locations are not updated to reflect the changed landscape, then stale images may be provided in response to a request for these images.
A determination of whether an information source is current may depend upon how frequently the information sources are updated. However, continuously observing any potential information sources to detect changes in content is an inefficient use of bandwidth resources since some information sources change frequently while other information sources are rarely modified. Further, as up-to-date information may be of greater value of many sources, it may also be inefficient to allocate bandwidth to refresh information sources which are known to be dated.